Math teacher and YouTube user School of Fish shows us how to derive the formula for the path made by a pen as it traces a hypotrochoid pattern.

TRIGGER WARNING: If you were severely traumatized by math in high school, you might want to avoid watching this video. However, if you are in therapy for Math Class PTSD, you may wish to try small doses of this video to benefit from the narrator’s calm, relaxing voice.

VIEWER WARNING: The more you know about math, the more you’ll appreciate this video. For example, if you have forgotten what a cosine is, it’s likely to go right over your head. In that case, perhaps you will sleep more easily knowing that someone has deconstructed the magic generated by all those toothed rings and wheels. Or not.